Polymerization catalyst system using di-se-butyl dimethyoxysilane for preparation of polypropylene

ABSTRACT

It has been discovered that using di-sec-butyldialkoxysilanes, such as di-sec-butyldimethoxysilane (DSBDMS), as external electron donors for Ziegler-Natta catalysts can provide a catalyst system that may prepare polypropylene films with improved properties and processing. The catalyst systems of the invention provide high activity, high bulk density, moderate hydrogen response, moderate donor response and high polydispersity (MWD). Suitable di-sec-butyldialkoxysilanes have the formula ( s Bu) 2 Si(OR″) 2 , where R″ is independently a straight or branched alkyl group of 1-5 carbon atoms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No.10/724,925, filed on Dec. 1, 2003, which claims the benefit of U.S.provisional application 60/483,215 filed Jun. 27, 2003.

FIELD OF THE INVENTION

The present invention relates to polymerization catalyst systems andprocesses for the preparation of polypropylene, and more particularlyrelates, in one embodiment, to polymerization catalyst systems for andcontrolled polymerization processes for the preparation of polypropylenethat gives improvement in physical properties.

BACKGROUND OF THE INVENTION

Thermoplastic olefin polymers, such as linear polyethylene,polypropylene, and olefin copolymers, are formed in polymerizationreactions where a monomer is introduced into a reactor with anappropriate catalyst to produce the olefin homopolymer or copolymer. Thepolymer is withdrawn from the catalyst reactor and may be subjected toappropriate processing steps and then extruded as a thermoplastic massthrough an extruder and die mechanism to produce the polymer as a rawmaterial in particulate form, usually as pellets or granules. Thepolymer particles are ultimately heated and processed in the formationof the desired end products.

Polypropylene manufacturing processes typically involve thepolymerization of propylene monomer with an organometallic catalyst ofthe Ziegler-Natta type. The Ziegler-Natta type catalyst polymerizes thepropylene monomer to produce predominantly solid crystallinepolypropylene. Polypropylene is most often produced as a stereospecificpolymer. Many desirable product properties, such as strength anddurability, depend on the crystallinity of the polypropylene that inturn is dependent on the stereospecific arrangement of methyl groups onthe polymer backbone.

Stereospecific polymers are polymers that have a defined arrangement ofmolecules in space. Both isotactic and syndiotactic propylene polymers,for example, are stereospecific. The isotactic structure is typicallydescribed as having the methyl groups attached to the tertiary carbonatoms of successive monomeric units on the same side of a hypotheticalplane through the main chain of the polymer, e.g., the methyl groups areall above or all below the plane.

This structure provides a highly crystalline polymer molecule. Using theFisher projection formula, the stereochemical sequence of isotacticpolypropylene may be shown as follows:

Another way of describing the structure is through the use of NMRspectroscopy. Bovey's NMR nomenclature for an isotactic pentad is mmmmwith each “m” representing a “meso” dyad or successive methyl groups onthe same side in the plane. As known in the art, any deviation orinversion in the structure of the chain lowers the degree ofisotacticity and crystallinity of the polymer.

This crystallinity distinguishes isotactic polymers from an amorphous oratactic polymer, which is more soluble in an aromatic solvent such asxylene. Atactic polymer exhibits no regular order of repeating unitconfigurations in the polymer chain and forms essentially a waxyproduct. That is, the methyl groups in atactic polypropylene arerandomly positioned. While it is possible for a catalyst to produce bothamorphous and crystalline fractions, it is generally desirable for acatalyst to produce predominantly crystalline polymer with very littleamorphous atactic polymer.

Catalyst systems for the polymerization of olefins are well known in theart. Typically, these systems include a Ziegler-Natta typepolymerization catalyst; a co-catalyst, usually an organoaluminumcompound; and an external electron donor compound or selectivity controlagent, usually an organosilicon compound. There are a number ofpublications relating to catalysts and catalyst systems designedprimarily for the polymerization of propylene and ethylene.

Ziegler-Natta catalysts for the polymerization of isotactic polyolefinsare well known in the art. The Ziegler-Natta catalysts arestereospecific complexes derived from a halide of a transition metal,such as titanium, chromium or vanadium with a metal hydride and/or metalalkyl, typically an organoaluminum compound as a co-catalyst. Thecatalyst is usually comprised of a titanium halide supported on amagnesium compound. Ziegler-Natta catalysts, such as titaniumtetrachloride (TiCl₄) supported on an active magnesium dihalide, such asmagnesium dichloride or magnesium dibromide, are supported catalysts.Silica may also be used as a support. The supported catalyst may beemployed in conjunction with a co-catalyst such as an alkylaluminumcompound, for example, triethyl aluminum (TEAL), trimethyl aluminum(TMA) and triisobutyl aluminum (TIBAL).

The development of these polymerization catalysts has advanced ingenerations of catalysts. The catalysts currently used are considered bymost to be third or fourth generation catalysts. With each newgeneration of catalysts, the catalyst properties have improved,particularly the efficiencies of the catalysts, as expressed inkilograms of polymer product per gram of catalyst over a particulartime.

In the utilization of a Ziegler-Natta catalyst for the polymerization ofpropylene, it is generally desirable to add an external donor. Externaldonors act as stereoselective control agents to control the amount ofatactic or non-stereoregular polymer produced during the reaction, thusreducing the amount of xylene solubles. Examples of external donorsinclude organosilicon compounds such as cyclohexylmethyldimethoxysilane(CMDS), dicyclopentyldimethoxysilane (CPDS) anddiisopropyldimethoxysilane (DIDS). External donors, however, tend toreduce catalyst activity and tend to reduce the melt flow of theresulting polymer.

In addition to the improved catalysts, improved activation methods havealso lead to increases in the catalyst efficiency. For example, onediscovery involved a process for pre-polymerizing the catalyst justprior to introducing the catalyst into the reaction zone.

It is generally possible to control catalyst productivity (i.e., lbs. ofpolypropylene/lb. catalyst or other weight ratios) and productisotacticity within limits by adjusting the molar feed ratio ofco-catalyst to external electron donor (and their corresponding ratiosto the active metal content, e.g., titanium, in the Ziegler-Nattacatalyst). Increasing the amount of external electron donor decreasesthe xylene solubles but may reduce activity and hence catalystproductivity. The xylene solubles (XS) content of the polypropyleneproduct is a measure of the degree of stereoselectivity. Further, thepolymer stereoregularity may be obtained by directly measuring themicrotacticity of the product via ¹³C Nuclear Magnetic Resonancespectroscopy. The crystalline fraction used for this analysis is theXIHI (xylene insoluble, heptane insoluble) fraction.

Selectivity to isotactic polypropylene is typically determined under theXS test by measuring the amount of polypropylene materials that arexylene soluble. The xylene-solubles were measured by dissolving polymerin hot xylene, cooling the solution to 0° C. and precipitating out thecrystalline material. The xylene solubles are the wt. % of the polymerthat was soluble in the cold xylene.

In particular with respect to film grade polyolefin resins for biaxiallyoriented polypropylene (BOPP) applications, there is continuing interestin identifying catalyst systems that offer potential improvements inpolymer physical properties and processability. Some previous studieshave focused on efforts to enhance resin processability/extrusioncharacteristics via broadening of polymer molecular weight distributionthrough utilization of particular donor types (e.g.,bis(perhydroisoquinolino)dimethoxysilane (BPIQ)). Other, more recentstudies have focused on the use of fluoroalkylsilane compounds (e.g.,3,3,3-trifluoro-propylmethyldimethoxysilane (“E” donor)) thatpotentially allow for a controlled lower polymer stereoregularity andslightly lower polymer melting temperature, thereby potentiallyimproving resin processability during film production. Indeed, thesevarious catalyst system approaches to the modification of polymerproperties for potential enhancement of film grade characteristics haveshown varying degrees of promise.

It would be particularly advantageous to discover additional usefulexternal donors and molar ratios of co-catalyst to external electrondonor in order to obtain desirable processing characteristics and obtainthe desirable amount of xylene solubles in polypropylene.

SUMMARY OF THE INVENTION

There is provided, in one form, a catalyst system for the polymerizationor copolymerization of propylene monomer having a Ziegler-Nattacatalyst, an organoaluminum compound co-catalyst, and at least oneexternal electron donor comprising di-sec-butyldimethoxysilane (DSBDMS).

In another embodiment of the invention, there is provided a process forthe polymerization or copolymerization of propylene monomer thatinvolves providing a Ziegler-Natta catalyst, contacting the catalystwith an organoaluminum compound, contacting the catalyst with at leastone electron donor comprising di-sec-butyldimethoxysilane (DSBDMS)simultaneously with or subsequent to contacting the catalyst with anorganoaluminum compound, introducing the catalyst into a polymerizationreaction zone containing the organoaluminum compound, the electron donorand propylene monomer, and optionally a chain length modifier (or chaintransfer reagent) such as hydrogen; and removing polypropylenehomopolymer or copolymer from the polymerization reaction zone.

In yet another embodiment of the invention, there is providedpolypropylene that encompasses a propylene polymer or copolymer having amelt flow (MF) of between about 1-100 decigrams/min. and xylene solublesof not more than about 6 weight %, and polydispersity (MWD) ranging fromabout 7 to about 11. In still another embodiment of the invention, theinvention concerns articles made from the polypropylene of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of catalyst activity as a function of specific donorand its concentration where hydrogen concentration was 0.40-0.43 mol %;

FIG. 2 is a graph of hydrogen response (melt flow as a function of mol %hydrogen) using various external electron donors at an Al/Si ratio of50;

FIG. 3 is a graph of donor response at various hydrogen levels forvarious electron donors where Al/Si=50; and

FIG. 4 is a graph of donor response for three electron donors at varioushydrogen and donor levels.

DETAILED DESCRIPTION OF THE INVENTION

It has been surprisingly discovered that a particular silane donormolecule, di-sec-butyldimethoxysilane, DSBDMS, (^(s)Bu)₂Si(OMe)₂, givesparticular advantage in the polymerization of propylene as part of aZiegler-Natta type catalyst system. The DSBDMS was then utilized as theexternal donor of a 4^(th)-generation Ziegler-Natta catalyst system topolymerize propylene. With respect to a standard external donor used,CMDS, it was found that DSBDMS effects high activity, high bulk density,moderate hydrogen response, moderate donor response, and high MWD. Sincea broad MWD polypropylene shows advantages in processing due to higherthroughput and finds use in BOPP film applications, DSBDMS hasparticular promise as a useful external electron donor. Additionally,the silane donor molecule, di-sec-butyldiethoxysilane, DSBDES,(^(s)Bu)₂Si(OEt)₂, displays advantageous character when used as part ofan alpha-olefin polymerization system. Furthermore, mixtures of DSBDMSand DSBDES, and by simple extension to (^(s)Bu)₂Si(OEt)(OMe), can beutilized to obtain advantageous character when used as part of analpha-olefin polymerization system.

In one particular non-limiting embodiment of the invention, the silanedonors of this invention can be described by the formula(^(s)Bu)₂Si(OR″)₂, where R″ is independently a straight or branchedalkyl group of 1-5 carbon atoms. Other specific examples of silanedonors within the method of this invention include (^(s)Bu)₂Si(OEt)₂ and(^(s)Bu)₂Si(OEt)(OMe), where Me and Et refer to methyl and ethyl,respectively, of course. In an alternate non-limiting embodiment of theinvention, R″ is methyl and/or ethyl.

The Ziegler-Natta catalysts useful in the present invention includethose derived from a halide of a transition metal, such as titanium,chromium or vanadium, with titanium being an advantageous metal in manyembodiments. Examples of transition metal compounds include, but are notnecessarily limited to, TiCl₄, TiBr₄, TiO(C₂H₅)₃Cl, Ti(OC₂H₅)₃Cl,Ti(OC₃H₇)₂Cl₂, TiO(C₆H₁₃)₂Cl₂, Ti(OC₂H₅)₂Br₂ and Ti(OC₁₂H₂₅)Cl₃. Thetransition metal compounds may be used individually or in combination.Typical titanium levels are from about 1.0% to about 5.0% by weight ofcatalyst, in one non-limiting embodiment of the invention. TheZiegler-Natta catalyst may be a transition metal compound of the formulaMR_(x) where M is selected from the group consisting of titanium,chromium, and vanadium, R is selected from the group consisting ofhalogen or a hydrocarboxyl, and x is an integer up to and including themaximum valence of M as dictated by its position in the Periodic Table.

The transition metal halide is used in combination with a metal hydrideand/or metal alkyl, typically an organoaluminum compound as aco-catalyst. Desirably the co-catalyst is an aluminum alkyl having theformula AlR₃, where R is an alkyl group having 1 to 8 carbon atoms, withR being the same or different. Examples of suitable aluminum alkylsinclude, but are not necessarily limited to, trimethyl aluminum (TMA),triethyl aluminum (TEAL) and triisobutyl aluminum (TIBAL). In onenon-limiting embodiment of the invention, the desired aluminum alkyl isTEAL.

In one non-limiting theory about the mechanism by which the inventionherein functions, the external donor operates by countering the loss ofinternal donor in the catalyst system. The nature of the internal donoris not particularly critical to the catalyst and its method of use inthis invention, as long as the goals and objectives of the inventionwith respect to the polypropylene product are met. Suitable internaldonors include, but are not necessarily limited to, diethers, aromaticdiesters such as alkyl phthalate donors (e.g. diethyl phthalate,di-isobutyl phthalate), amines, amides, ketones, nitriles, phosphines,thioethers, thioesters, aldehydes, alcoholates, salts of organic acids,succinates, malonates, oxalates, glutarates and combinations thereof.One useful group of internal donors includes, but is not necessarilylimited to, esters of phthalic acid such as di-isobutyl, dioctyl,diphenyl, di-n-butyl, di-2-ethylhexyl, and benzylbutyl, and the like,and combinations thereof.

These internal electron donors are added during the preparation of thecatalysts and may be combined with the support or otherwise complexedwith the transition metal halide.

The Ziegler-Natta catalyst is typically a supported catalyst. Suitablesupport materials include magnesium compounds, such as magnesiumhalides, dialkoxymagnesiums, alkoxymagnesium halides, magnesiumoxyhalides, dialkylmagnesiums, magnesium oxide, magnesium hydroxide, andcarboxylates of magnesium. Typical magnesium levels are from about 10%to about 25% by weight of catalyst.

In the subject invention, the Ziegler-Natta catalyst must be used withat least one external donor compound, such as a Lewis base. Morespecifically, external donors are typically organosilicon compounds.External electron donors may be those described by the formulaSiR_(m)(OR′)_(4-m), where R is an alkyl group, a cycloalkyl group, anaryl group or a vinyl group, R′ is an alkyl group, m is 0-4, each R′ maybe the same or different, and each R may be the same or different. Inparticular, the external electron donor acts as a stereoregulator and tocontrol the amount of atactic form of polymer produced, which results ina decrease in xylene solubles. That is, external electron donors canboth affect the isotacticity of a polymer chain produced by a specificactive site and inhibit or “shut down” atactic active sites.Representative examples of external donors includecyclohexylmethyldimethoxysilane (CMDS), dicyclopentyldimethoxysilane(CPDS), diisopropyldimethoxysilane (DIDS),cyclohexylisopropyldimethoxysilane (CIDS), di-t-butyldimethoxysilane(DTDS), (3,3,3-trifluoropropyl)methyldimethoxysilane (“E” donor), andcombinations thereof. However, in the subject invention, at least one ofthe electron donors that should be used is di-sec-butyldimethoxysilane(DSBDMS). As discussed, DSBDMS has been discovered to be used withZiegler-Natta catalysts to provide high catalyst activity, high bulkdensity, moderate hydrogen response, moderate donor response, and highMWD (polydispersity), and hence improved processing due to higherthroughput, particularly for BOPP film. It is within the scope of thisinvention to use DSBDMS in conjunction with one or more other externaldonors including, but not necessarily limited to, CMDS, CPDS, DIDS,CIDS, DTDS and/or “E” donor. In some cases it will be found that thereis a synergistic effect between the internal donor and the externaldonor. That is, results will be obtained with a particular combinationof internal donor and external donor that cannot be achieved with one orthe other individually.

Unless specified otherwise, amounts of external donor are presentedherein as parts per million (ppm) based on the weight of monomer. In onenon-limiting embodiment of the invention, the amount of DSBDMS rangesfrom about 0.5 to about 500 ppm, alternatively from about 0.5 to about200 ppm, and in another non-limiting embodiment from about 0.5 to about20 ppm. Desirably, any second or subsequent external donor is used inthe range of from about zero to about 200 ppm, and in anothernon-limiting embodiment from about 0 to about 100 ppm. The Al/Si molarratio (organoaluminum compound to silane donor) may range from about 0.5to about 500, and in another non-limiting embodiment from about 0.5 toabout 100 ppm, and in another non-limiting embodiment from about 0.5 toabout 20 ppm.

As is well known, polypropylene may be produced by slurry polymerizationin the presence of a solvent, e.g. hexane, such as in a loop or CSTRreactor, or by bulk polymerization in which propylene serves as bothmonomer and diluent, which is typically carried out in a loop-typereactor. Also, polypropylene may be produced by gas phase polymerizationof propylene, which is typically carried out in a fluidized bed reactorunder lower pressures than bulk polymerization. In a typical bulkprocess, one or more loop reactors operating generally from about 50 toabout 100° C. (in another non-limiting embodiment from about 60 to about80° C.), with pressures of from about 300 to 700 psi (2.1 to 4.8 MPa)(from about 450 to about 650 psi in another non-limiting embodiment)(3.1 to 4.5 MPa), may be used to polymerize propylene. The variouscatalytic components, i.e., Ziegler-Natta catalyst, cocatalyst, externaldonor, are introduced into the reactor, as well as a molecular weightcontrolling agent (if any, e.g., hydrogen), and the resultingpolypropylene fluff or powder is continuously removed from the reactor.The fluff may then be subjected to extrusion to produce desired pellets.Suitable molecular weight modifiers include, but are not necessarilylimited to, hydrogen.

In the study of this invention, a conventional titanium supported on anactive magnesium dihalide Ziegler-Natta catalyst was used in thepresence of a number of external silane donors to assess effects onpolymerization performance and polymer properties.

For bulk polymerization utilizing the DSBDMS external donor-containingcatalyst, the reactor temperatures are usually kept from about 50 toabout 100° C., more particularly from about 60° C. to about 80° C. inone non-limiting embodiment. It should be noted that increasing thetemperature (within limits) will typically result in an increasedcatalytic activity and lower xylene solubles. Hydrogen concentrationsmay vary, but are usually kept at from about 0.02 mol % to about 1.1 mol%, in one non-limiting embodiment from about 0.04 mol % to about 0.5 mol% based on monomer, and depending on the resin melt flow desired.

The polymers produced in accordance with the present invention are thosehaving a melt flow after polymerization of at least 1 decigram/min orgreater, as measured according to ASTM D1238-95. Typical melt flowsuseful for preparation of BOPP film are from about 1 to about 100decigram/min, with from about 1 to about 16 decigram/min being readilyobtainable, under the stated conditions while still retaining low xylenesolubles. Thus, the polymers of this invention are expected to besuitable for film grade resins as well as for injection moldingapplications, and the like. The polymers produced are also characterizedas having low xylene solubles of not more than about 6 weight %, fromabout 0.5 to about 6 wt % in an alternate, non-limiting embodiment ofthe invention, with from about 1 to about 5% being readily obtainable,and from 1 to about 4% being more readily obtainable, without anydetrimental effects on melt flow.

Additionally, the polypropylene homopolymer or copolymer may have ameson pentad level of between about 95 to about 98 wt. % as measured via¹³C NMR on the insoluble (i.e., crystalline) fraction. While thisisotacticity gained from use of DSBDMS, is not necessarily ideal forBOPP film, these levels are closer to what is commonly called highcrystallinity polypropylene, HCPP. The resin obtained from use of DSBDMSmay have attributes advantageous for use in some cases of BOPP and somecases of HCPP. The polydispersity (Mw/Mn) of the polypropylenehomopolymer or copolymer, as measured via Size Exclusion Chromatography,may range from about 7 to about 11, in another non-limiting embodimentfrom about 9 to about 11.

As used herein, the terms “propylene polymer” or “polypropylene,” unlessspecified otherwise, shall mean propylene homopolymers or those polymerscomposed primarily of propylene and limited amounts of other comonomers,such as ethylene, wherein the comonomers make up less than 0.5% byweight of polymer, and more typically less than 0.1% by weight ofpolymer. However, in some cases, minirandom copolymers with even smallamounts of ethylene are desired. The catalyst components of thisinvention provide another way of adjusting the microtacticity of thepolypropylene and thus improving the properties of film gradepolypropylene.

The following examples serve to illustrate the present invention, butare not intended to limit the invention in any way.

The polymerization experiments were performed with Toho THC A (aconventional 4^(th)-generation titanium containing propylenepolymerization catalyst available from Toho Catalyst Co., Ltd.) understandard conditions: 1 hr polymerization, 70° C., in situprepolymerization.

(^(s)Bu)₂Si(OMe)₂ preparation: A round bottom flask was charged withSi(OMe)₄ (100 mmol) and hexane (30 mL) and cooled to 0° C. Over sevenhours, ^(s)BuMgCl (60 mmol, 2.0 M in Et₂O) was added drop-wise. Themixture was then stirred at ambient temperature overnight andsubsequently purified by thermal distillation.

(^(s)Bu)₂Si(OEt)₂ preparation: A round bottom flask was charged withSiCl₄ (47 mmol) and hexane (50 mL) and cooled to 0° C. Over four hours,^(s)BuMgCl (99 mmol, 2.0 M in Et₂O) was added dropwise. The mixture wasthen stirred at ambient temperature for 30 minutes and then cooled to 0°C. A mixture of ethanol (114 mmol) and pyridine (101 mmol) was added andthe mixture was allowed to warm to ambient temperature and subsequentlypurified by thermal distillation.

The donor DSBDMS, when compared to diisopropyl dimethoxysilane (DIDS),generally imparts higher XS, MF, and MWD. The diethoxy homolog ofDSBDMS, DSBDES, imparts desirable polymer properties as well with veryhigh MF, rather high XS, and moderate MWD. Furthermore, mixtures ofDSBDMS and DSBDES impart polymer properties with some synergism seenwith XS, activity, and MWD.

The general experimental conditions and reagents for the catalystevaluations are shown in Table I. The comparative resins produced havethe characteristics and properties shown in Table II. TABLE IExperimental Conditions for Catalyst Evaluations Reagents: Conditions:Catalyst: 10 mg Temp.: 70° C. TEAL: 1.0 mmol Time: 1 hour Ext. Donor:0.10 or 0.02 mmol Propylene: 1.4 L (0.74 kg) Prepolymerization: in situ

TABLE II Polymerization Data and Comparisons H₂ XS MF MWD Activity mmmmBD Ex. Donor Al/Si (mol %) (wt %) (dg/min) (Mw/Mn) (g/g/h) (mol %)(g/cm³) 1 CMDS 10 0.08 1.16 1.7 6.7 33,200 0.48 2 CMDS 10 0.40 1.44 10.0— 36,200 0.49 3 CMDS 50 0.08 3.12 3.0 — 36,600 0.45 4 CMDS 50 0.40 4.7024.0 6.7 46,000 96.1 0.45 9 DIBDS 10 0.09 1.56 2.9 8.2 32,600 0.47 10DIBDS 20 0.43 2.04 11.8 9.0 45,000 0.49 11 DIBDS 50 0.09 3.04 4.2 9.140,500 95.7 0.47 12 DIBDS 50 0.43 2.48 22.7 8.1 44,200 0.47 13 CPDS 100.08 1.0 0.5 9.1 34,800 0.49 14 CPDS 10 0.40 1.24 4.5 — 46,800 0.49 15CPDS 50 0.08 1.4 0.7 — 34,800 0.49 16 CPDS 50 0.40 1.6 4.2 7.8 45,80097.6 0.49 17 DIDS 10 0.09 1 1.20 7.3 38,000 0.49 18 DIDS 10 0.43 1.28.60 8.2 43,300 0.48 19 DIDS 50 0.09 1.04 1.0 8.3 38,800 97.1 0.50 20DIDS 50 0.43 1.52 7.3 9.8 46,000 0.49 21 DSBDMS 10 0.09 1.6 1.5 9.531,000 0.48 22 DSBDMS 10 0.43 1.7 15.5 8.4 39,200 0.49 23 DSBDMS 50 0.091.4 1.8 9.1 34,500 95.6 0.49 24 DSBDMS 50 0.43 2.2 13.0 9.4 44,000 0.4825 DSBDES 10 0.09 11.46 15.1 7.7 31,800 0.40 26 DSBDES 10 0.43 10.0 93.06.5 40,200 0.41 27 DSBDES 50 0.09 16.4 22.0 6.1 32,300 0.34 28 DSBDES 500.43 13.7 140.0 6.7 40,500 94.3 0.38 29 1:1 10 0.43 1.92 17 8.7 41,3000.48 DSBDMS:DSBDES

FIG. 1 is a graph of catalyst activity as a function of Al/Si ratio at10 and 50 for of the donors, where the hydrogen concentration was fromabout 0.40 to about 0.43 mol. %. FIG. 2 is a graph of hydrogen response(melt flow as a function of mol % hydrogen) using various externalelectron donors at an Al/Si ratio of 50. FIG. 3 is a graph of donorresponse at various hydrogen levels for a variety of electron donorsexpressed as xylene solubles in wt. % as a function of mol % hydrogenpresent, where the Al/Si ratio was 50. FIG. 4 is a graph of donorresponse at various hydrogen and donor levels expressed as melt flow indg/min for CPDS, DSBDMS and DSBDES electron donors.

It is of interest to note that the activity of DSBDMS is only about 5%lower than that of the conventional CMDS. It may be seen that DSBDMSprovides relatively high catalyst activity, relatively high bulk density(BD), relatively high polydispersity, while also yielding relativelymoderate hydrogen response and moderate donor response.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing a Ziegler-Natta catalyst system for thepolymerization and copolymerization of propylene monomer. However, itwill be evident that various modifications and changes can be madethereto without departing from the broader spirit or scope of theinvention as set forth in the appended claims. Accordingly, thespecification is to be regarded in an illustrative rather than arestrictive sense. For example, specific combinations or amounts ofcatalysts, co-catalysts, internal donors, and external donors, and othercomponents and proportions thereof falling within the claimedparameters, but not specifically identified or tried in a particularcatalyst system, are anticipated and expected to be within the scope ofthis invention. Further, the method of the invention is expected to workat other conditions, particularly temperature, pressure andconcentration conditions, than those exemplified herein.

1. A catalyst system for the polymerization or copolymerization ofolefins comprising: a Ziegler-Natta catalyst; an organoaluminum compoundco-catalyst; and at least one external electron donor comprising adi-sec-butyldialkoxysilane having the formula (^(s)BU)₂Si(OR″)₂, whereR″ is independently a straight or branched alkyl group of 1-5 carbonatoms.
 2. The catalyst of claim 1 where the Ziegler-Natta catalystcomprises a transition metal compound of the formula MR_(x) where M isselected from the group consisting of titanium, chromium, and vanadium,R is selected from the group consisting of halogen or a hydrocarboxyl,and x is an integer up to and including the maximum valence of M asdictated by its position in the Periodic Table.
 3. The catalyst of claim1 where in contacting the catalyst with an organoaluminum compound, theorganoaluminum compound is triethyl aluminum (TEAL).
 4. The catalyst ofclaim 1 where the Al/Si molar ratio (organoaluminum compound to silanedonor) ranges from about 0.5 to about
 500. 5. The catalyst of claim 1where the external electron donor is selected from the group consistingof di-sec-butyldimethoxysilane (DSBDMS), di-sec-butyldiethoxysilane(DSBDES), di-sec-butylmethoxyethoxysilane, and mixtures thereof.
 6. Acatalyst system for the polymerization or copolymerization of olefinscomprising: a Ziegler-Natta catalyst, where the Ziegler-Natta catalystcomprises a transition metal compound of the formula MR_(x) where M isselected from the group consisting of titanium, chromium, and vanadium,R is selected from the group consisting of halogen or a hydrocarboxyl,and x is an integer up to and including the maximum valence of M asdictated by its position in the Periodic Table; an organoaluminumcompound co-catalyst; and at least one external electron donor selectedfrom the group consisting of di-sec-butyldimethoxysilane (DSBDMS),di-sec-butyldiethoxysilane (DSBDES), di-sec-butylmethoxyethoxysilane,and mixtures thereof, where the Al/Si molar ratio (organoaluminumcompound to silane donor) ranges from about 0.5 to about
 500. 7. Thecatalyst of claim 6 where the organoaluminum compound is triethylaluminum (TEAL).
 8. Polypropylene comprising a propylene polymer orcopolymer having a melt flow ranging from about 1-100 decigrams/min., apolydispersity ranging from about 7 to about 11, and xylene solublesranging from about 0.5 to about 6 wt %.
 9. Polypropylene formed by aprocess comprising: providing a Ziegler-Natta catalyst, and in anyorder: contacting the catalyst with an organoaluminum compound;contacting the catalyst with at least one electron donor comprising adi-sec-butyldialkoxysilane simultaneously with or subsequent tocontacting the catalyst with an organoaluminum compound, where thedi-sec-butyldialkoxysilane has the formula (^(s)Bu)₂Si(OR″)₂, where R″is independently a straight or branched alkyl group of 1-5 carbon atoms;introducing the catalyst into a polymerization reaction zone containingthe organoaluminum compound, the electron donor and propylene monomer;and removing polypropylene homopolymer or copolymer from thepolymerization reaction zone.
 10. The polypropylene of claim 9 where thepolypropylene has a higher polydispersity and higher bulk density ascompared to an otherwise identical polypropylene formed in the absenceof a di-sec-butyldialkoxysilane.
 11. An article formed frompolypropylene comprising a propylene polymer or copolymer having a meltflow ranging from about 1-100 decigrams/min. and xylene solubles of notmore than about 6% formed by a process comprising: providing aZiegler-Natta catalyst, and in any order: contacting the catalyst withan organoaluminum compound; contacting the catalyst with at least oneelectron donor comprising a di-sec-butyldialkoxysilane simultaneouslywith or subsequent to contacting the catalyst with an organoaluminumcompound, where the di-sec-butyldialkoxysilane has the formula(^(s)Bu)₂Si(OR″)₂, where R″ is independently a straight or branchedalkyl group of 1-5 carbon atoms; introducing the catalyst into apolymerization reaction zone containing the organoaluminum compound, theelectron donor and propylene monomer; and removing polypropylenehomopolymer or copolymer from the polymerization reaction zone.
 12. Thearticle of claim 11 where the article is biaxially orientedpolypropylene (BOPP) film.
 13. The article of claim 11 where the articleis high crystallinity polypropylene (HCPP).